Question

On what principle does the Sun-dial work?

Answer 1

Sundials work from the shadow movement of a fixed object based on varying positions of the Sun throughout the day. It tells the time of day by the apparent position of the Sun in the sky. It consists of a flat plate (the dial) and a gnomon, which casts a shadow onto the dial. As the Sun appears to move across the sky, the shadow aligns with different hour-lines, which are marked on the dial to indicate the time of the day.